While I can't tell you what law schools are going to think, my personal opinion is that you're going to want letters of recommendation that each say something unique about you as a candidate. If two computer science professors have had different experiences with you, I would say go for it; if they are going to both say "M2 was a good student in my computer science class" I think it would be better to get one from someone else. I'll tell you my strategy and see if it gives you any help.
I'm an engineer and have talked to a bunch of admissions officers about how engineers are perceived, what they see as weakenesses and strength, etc. The theme I have gotten is that engineers are hard workers with good analytical skills, but that admissions officers are worried about their ability to communicate and to do well in a non-technical field like law. To combat the communications stigma, I had my technical writing professor (who used to teach English) write a letter talking about my writing skills and my public speaking ability. My second letter of recommendation is coming from a professor I took for a Philosophy of Law class; I made sure I contributed a LOT in his class, and also wrote a completely unrequested paper based off a question I asked him about drug addiction and the insanity defense. I spent many, many hours in the law library doing research for this paper, and I think he was really impressed when one day I just dropped in to office hours and handed it to him. Finally, I've TAed for an engineering class for the past three years, and I'm going to have the professor I worked with submit a letter regarding those experiences. While this won't directly combat any of the engineering stigmas, I plan on writing my personal essay on my experiences working there, and I think a letter of rec from him will help flesh out that part of my app.
Anyway, just my opinion on the matter. It probably doesn't matter WHO you get a letter from as much as what they say.